PROJECT SUMMARY The thalamic reticular nucleus (TRN) is a critical brain region that greatly influences vital neurobehavioral processes, including attention and the generation of sleep rhythms. Most recently, TRN dysfunction was suggested to underlie hyperactivity, attention deficits, and sleep disturbances observed across various devastating neurodevelopmental disorders, including autism, schizophrenia and attention-deficit/hyperactivity disorder (ADHD). Notably, a highly specialized sarco-endoplasmic reticulum calcium (Ca2+) ATPase 2 (SERCA2)-dependent Ca2+ signaling network operates in the dendrites of TRN neurons to generate and regulate their high-frequency bursting activity. Phospholamban (PLN) is a crucial regulator of the SERCA2 with an established role in maintaining Ca2+ homeostasis in the heart. Though the interaction of PLN with SERCA2 has been largely regarded as cardiac-specific, exciting preliminary data from our laboratory challenge this view and suggest that the role of PLN extends beyond the cardiovascular system to impact the function of TRN neurons. Specifically, solid preliminary evidence indicates that PLN protein is selectively expressed in the TRN neurons of the adult mouse brain and that constitutive loss of PLN function in mice (PLNKO) results in hyperactivity and cognitive deficits. Our overarching hypothesis is that PLN is a prominent Ca2+-handling player in the TRN neurocircuitry involved in regulating the firing activity of TRN neurons and critical TRN- dependent behaviors. To test this hypothesis, we will use constitutive and innovative conditional genetic mouse models, in combination with sophisticated electrophysiological (i.e., whole-cell patch-clamping) and behavioral approaches (i.e., the 5-choice serial-reaction time task; 5-CSRTT, and electroencephalography- based polysomnography) to assess the role of PLN in regulating the burst-firing activity of TRN neurons, as well as attention and sleep, two complex behaviors that map onto thalamic reticular circuits. The studies outlined in the current NIH Small Research Grant (R03) proposal will functionally isolate the TRN as a brain region where PLN regulates attention and sleep by affecting specific cellular processes. Performing this research will enable future experiments aimed at more intensive dissection of the molecular and cellular mechanisms implicated in the regulation of the PLN/SERCA2 pathway in TRN neurons, and will lay the groundwork for considering PLN as a novel Ca2+-handling player in brain physiology and pathophysiology.